The Panchromatic Afterglow of GW170817: The full uniform dataset, modeling, comparison with previous results and implications

Abstract

We present the full panchromatic afterglow light curve data of GW170817, including new radio data as well as archival optical and X-ray data, between 0.5 and 940 days post-merger. By compiling all archival data, and reprocessing a subset of it, we have evaluated the impact of differences in data processing or flux determination methods used by different groups, and attempted to mitigate these differences to provide a more uniform dataset. Simple power-law fits to the uniform afterglow light curve indicate a $t^{0.86\pm 0.04}$ rise, a $t^{-1.92\pm 0.12}$ decline, and a peak occurring at $155\pm 4$ days. The afterglow is optically thin throughout its evolution, consistent with a single spectral index ($-0.584\pm 0.002$) across all epochs. This gives a precise and updated estimate of the electron power-law index, $p=2.168\pm 0.004$. By studying the diffuse X-ray emission from the host galaxy, we place a conservative upper limit on the hot ionized ISM density, $<$0.01 cm${}^{-3}$, consistent with previous afterglow studies. Using the late-time afterglow data we rule out any long-lived neutron star remnant having magnetic field strength between 10${}^{10.4}$ G and 10${}^{16}$ G. Our fits to the afterglow data using an analytical model that includes VLBI proper motion from Mooley et al. (2018), and a structured jet model that ignores the proper motion, indicates that the proper motion measurement needs to be considered while seeking an accurate estimate of the viewing angle.

Accepted by ApJ. Revised X-ray and up-to-date afterglow measurements are available in ASCII format on GitHub (https://github.com/kmooley/GW170817/) and mirrored on tauceti.caltech.edu (http://www.tauceti.caltech.edu/kunal/gw170817/). The online dataset will be continuously updated as new measurements become available

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• What determines the structure of short gamma-ray burst jets?
• Impact of the ISM magnetic field on GRB afterglow polarization
• Late-time radio observations of the short GRB200522A: constraints on the magnetar model
• Late-Time Evolution and Modeling of the Off-Axis Gamma-ray Burst Candidate FIRST J141918.9+394036
• Short duration gamma-ray bursts and their outflows in light of GW170817
• Infrared dust echoes from neutron star mergers
• Accurate flux calibration of GW170817: is the X-ray counterpart on the rise?
• Are Interactions with Neutron Star Merger Winds Shaping the Jets?